Depth annotation is an important part of submarine topography mapping, chart drawing and marine engineering drawing. Bathymetric chart is capable to quantitatively describe topography and geomorphology of submarine, and intuitively reflect the navigation capacity of sea area. Bathymetric chart plays a role that can't be replaced by other charts in scientific research and navigation. The difference between a bathymetric chart and other topographical maps is that the representation of a bathymetric chart mainly relies on depth annotations with subsidiary isobath, combined with substrate annotations. Depth is the main parameter to reflect topographic relief.
The single-beam echo sounding obtains less bathymetric data, and most of raw data are retained when mapping bathymetric chart. Its disadvantage is the sparse of the data which leads to missing submarine topographic feature points. Now the single-beam echo sounding is rarely used in high-resolution seafloor detection. High-density multi-beam echo sounding (MBES) are currently the highest-resolution representation of the morphology of seafloor. With the aid of the full-coverage technology, high-resolution sounding data are obtained, and large-scale bathymetric charts are derived. But a notable feature of MBES is the large amount of the high-resolution sounding data. So in accordance with the principle of depth annotations, a series of raw sounding data that meet mapping requirements should be selected from the large amount of sounding data.
Currently there are mainly two ways to draw bathymetric charts based on multi-beam soundings: using grid data directly, or using the central beam. Both of them are limited in use. The disadvantage of using grid data directly is that the measured data are not employed; negatively affecting the reliability of the maps; while using the central beam tends to miss the feature depth points of survey lines which need to be identified.
Full use of the raw multi-beam sounding data to construct bathymetric chart is not identified in the art and remains to be answered.